1. Field of the Invention
This invention relates to the field of modulating (proportioning) electromagnetic control valves used to control gas or fluid flow rates in high-performance applications.
2. Material Information
Known electromagnetic modulating valves use a soft iron armature for the moving part of the valve. A magnetic field produced by an electromagnet (solenoid) coil provides a tractive force between the armature and an iron pole piece, usually in a direction that tends to open the valve. This force is always in the same direction when current of either polarity is passed through the coil. This force is nominally proportional to the square of coil current (until iron saturation phenomena occur). One or more springs produce forces that oppose the solenoid force. The net force applied to the armature is thus the difference between the solenoid and spring forces. The armature movement is proportional to the net force applied to it and inversely proportional to the spring rates of the mechanical springs between the armature and housing. For smooth operation the mechanical design requires low friction which consequently results in low damping. During fast dynamic transient operation the valve can overshoot and then oscillate at its natural spring-mass frequency without convenient means for achieving stability.
For example, in the related application (FIG. 9) an armature 84 having flow passages 84a therein is movable against end springs 84b, 85a to seat and unseat a valve seal on an orifice 97. An armature coil 95 surrounds armature 84 and flow of current dictated by a sensed flow in a flow channel moves the armature to regulate gas flow through the orifice. Upon cessation of current flow the valve seal returns to a fail-safe closed position against the orifice.
Many solenoid valves have been designed with permanent magnets in the armature for the purpose of achieving bistable or "latching" operation. These are not modulating valves because they do not operate over a continuously variable range of stable positions, and hence are not pertinent to the present invention.
Known modulating valves use a compliant elastomeric sealing disk attached to the armature by chemical bonding or mechanical retention. Chemically resistant elastomers are difficult to bond to the armature and, if bonded, suffer from reduced resistance to chemical attack in the bond area. Mechanical retention methods include insertion of a relatively thick and oversized sealing disk into a cavity with reentrant side walls or alternatively the sealing disk may be mechanically clamped around its perimeter.